Body size is negatively correlated with trophic position among cyprinids

Abstract

Body size has many ecological and evolutionary implications that extend across multiple levels of organization. Body size is often positively correlated with species traits such as metabolism, prey size and trophic position (TP) due to physiological and mechanical constraints. We used stable isotope analysis to quantify TP among minnows across multiple assemblages that differed in their species composition, diversity and food web structure. Body size significantly predicted TP across different lineages and assemblages, and indicated a significant negative relationship. The observed negative relationship between body size and TP is contrary to conventional knowledge, and is likely to have arisen owing to highly clade-specific patterns, such that clades consist of either large benthic species or small pelagic species. Cyprinids probably subvert the physiological and mechanical constraints that generally produce a positive relationship between body size and TP using anatomical modifications and by consuming small-bodied prey, respectively. The need for herbivorous cyprinids to digest cellulose-rich foods probably selected for larger bodies to accommodate longer intestinal tracts and thereby to facilitate digestion of nutrient-poor resources, such as algae. Therefore, body size and TP are likely to have coevolved in cyprinids in association with specialization along the benthic to pelagic resource axis.

Body size–trophic position relationships among fishes of the lower Mekong basin

“…The body size–TP relationship was positive and significant for Mekong Perciformes and Siluriformes, groups dominated by species that ingest relatively large food items and therefore may often be gape limited, and was weaker and non-significant for Mekong Cypriniformes, a group that contains many microphagous detritivores and insectivores that span a wide range of body sizes ( figure 1 ) [ 40 ]. The regression slope for cypriniforms was negative, a finding consistent with studies of cypriniforms from other regions [ 14 , 20 ]. In addition to large cypriniforms that feed at low trophic positions, the lack of correlation between body size and TP in the cypriniform assemblage dataset ( figure 4 ) also is influenced by the presence of small species with relatively high TPs.…”

“…The lack of relationship between body size and TP in cyprinids has been attributed to their evolutionary history [ 20 , 46 , 47 ]. German et al .…”

“…[ 15 ], who investigated relationship between body size and δ 15 N (an index of relative TP) using long-term data (40 years) for freshwater fishes from Lake Biwa, Japan. Although there is ample evidence of positive relationships between body size and TP of fishes, other studies have shown no relationship between TP and size [ 16 – 18 ] or a negative relationship [ 19 , 20 ], which suggests that phylogeny and associated morphological and behavioural constraints also influence how body size affects species interactions [ 20 , 21 ]. Thus, even though the body size–TP relationship in fishes appears to be strongly influenced by gape limitation [ 13 , 22 ], other morphological traits could play roles [ 14 ].…”

Habitat disruption and the identification and management of functional trait changes

“…Although size structuring is not influenced by predatory or competitive interactions between native and introduced fishes in this system, it is likely that a variety of ecological and evolutionary mechanisms influence community dynamics and ecosystem processes (Fritschie & Olden, ). Regular evaluation of the population size structure may provide a cheap and simple way of monitoring food web structure, as body size is usually positively (Romanuk, Hayward, & Hutchings, ), but sometimes negatively (Burress, Holcomb, Bonato, & Armbruster, ) correlated with a species’ trophic position. Importantly, quantifying both intra‐ and interspecific variations in body size can serve as an important indicator of niche overlap and the functional variation (or redundancy) present in a community (Guillemot, Kulbicki, Chabanet, & Vigliola, ; Micheli & Halpern, ).…”

Ecological diversification associated with the benthic‐to‐pelagic transition by North American minnows

“…For example, ancient rivers such as White's River and the Appalachian River may have served as the sites of early minnow diversification and assemblage formation during periods of rapid sea level fluctuations during the Pleistocene (Nagle & Simons, ). Minnow assemblages exhibit diverse morphologies, trophic ecologies and habitat preferences (Burress et al ., ,b). An ancestral benthic‐to‐pelagic habitat shift that occurred around the Eocene–Oligocene border is hypothesized to have coincided with a burst in minnow species diversification (Hollingsworth et al ., ).…”